Could it be cancer?

I am 23 years old and worried that I may have lung cancer. I have smoked canabis for the last 5 years (3-4 joints a day) but quit this Thanksgiving because I began coughing and was spitting blackish phlegm. Since then my cough has disappeared although I still spit phlegm regularly(it is now clear or yellowish, especially after eating).

I was hoping this was going to decrease with time, but this morning there were some slight traces of blood in the spit. I do not have bronchitis, nor TD, so I am worried that it could be cancer.

If this were the case wouldn't the blood be apparent during the period I was smoking instead of 2 months down the line? Is it normal to have the phlegm production persist for a long period after stopping smoking? Is it possible to have lung/throat cancer at such an early age?

Your opinion is grately appreciated.

[National Jewish]

Since you quit smoking just 2 months ago, it is very likely that the slight traces of blood in your phlegm are a result of inflammation still present in your lungs from your past smoking.  As you go longer without smoking, you should have fewer traces of blood in your phlegm.  The blood need not have been apparent while smoking.
It is normal to have phlegm production continue, sometimes indefinitely, after quitting smoking.
It is unlikely to have lung and/or throat cancer at such an early age, but possible especially after smoking.  For this reason you should have a chest x-ray and a thorough examination of your nose, throat and larynx, by an ear nose and throat (ENT) specialist.